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Sulphate-reducing microorganisms, or SRMs, are crucial to organic decomposition, the sulphur cycle, and the formation of pyrite. Despite their low energy-yielding metabolism and intense competition with other microorganisms, their ability to thrive in natural habitats often lacking sufficient substrates remains an enigma. This study delves into how Desulfovibrio desulfuricans G20, a representative SRM, utilizes photoelectrons from extracellular sphalerite (ZnS), a semiconducting mineral that often coexists with SRMs, for its metabolism and energy production. Batch experiments with sphalerite reveal that the initial rate and extent of sulphate reduction by G20 increased by 3.6 and 3.2 times respectively under light conditions compared to darkness, when lactate was not added. Analyses of microbial photoelectrochemical, transcriptomic, and metabolomic data suggest that in the absence of lactate, G20 extracts photoelectrons from extracellular sphalerite through cytochromes, nanowires, and electron shuttles. Genes encoding movement and biofilm formation are upregulated, suggesting that G20 might sense redox potential gradients and migrate towards sphalerite to acquire photoelectrons. This process enhances the intracellular electron transfer activity, sulphur metabolism, and ATP production of G20, which becomes dominant under conditions of carbon starvation and extends cell viability in such environments. This mechanism could be a vital strategy for SRMs to survive in energy-limited environments and contribute to sulphur cycling., (© 2024 John Wiley & Sons Ltd.)

The end-Permian mass extinction represents the most severe biotic crisis for the last 540 million years, and the marine ecosystem recovery from this extinction was protracted, spanning the entirety of the Early Triassic and possibly longer. Numerous studies from the low-latitude Paleotethys and high-latitude Boreal oceans have examined the possible link between ocean chemistry changes and the end-Permian mass extinction. However, redox chemistry changes in the Panthalassic Ocean, comprising ∼85-90% of the global ocean area, remain under debate. Here, we report multiple S-isotopic data of pyrite from Upper Permian-Lower Triassic deep-sea sediments of the Panthalassic Ocean, now present in outcrops of western Canada and Japan. We find a sulfur isotope signal of negative Δ 33 S with either positive δ 34 S or negative δ 34 S that implies mixing of sulfide sulfur with different δ 34 S before, during, and after the end-Permian mass extinction. The precise coincidence of the negative Δ 33 S anomaly with the extinction horizon in western Canada suggests that shoaling of H 2 S-rich waters may have driven the end-Permian mass extinction. Our data also imply episodic euxinia and oscillations between sulfidic and oxic conditions during the earliest Triassic, providing evidence of a causal link between incursion of sulfidic waters and the delayed recovery of the marine ecosystem.

Global fossil data show that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale at the end of the Permian. Many hypotheses have been proposed to explain this extinction and yet still remain greatly debated. Here, we report analyses of all four sulphur isotopes ((32)S, (33)S, (34)S and (36)S) for pyrites in sedimentary rocks from the Meishan section in South China. We observe a sulphur isotope signal (negative δ(34)S with negative Δ(33)S) that may have resulted from limitation of sulphate supply, which may be linked to a near shutdown of bioturbation during shoaling of anoxic water. These results indicate that episodic shoaling of anoxic water may have contributed to the profound biodiversity crisis before the final catastrophe. Our data suggest a prolonged deterioration of oceanic environments during the Late Permian mass extinction.

Fe speciation and S-isotope of pyrite data from the terminal Proterozoic Sheepbed Formation in Canada and Doushantuo Formation in China reveal that ocean deep waters were anoxic after the global glaciations (snowball Earth) ending 635 million years ago, but that marine sulfate concentrations and inferentially atmospheric oxygen levels were higher than before the glaciations. This supports a long-postulated link between oxygen levels and the emergence of eumetazoa. Subsequent ventilation of the deep ocean, inferred from shifts in Fe speciation in Newfoundland (previously published data) and western Canada (this report), paved the way for Ediacaran macrobiota to colonize the deep seafloors.

Abstract: Microscopic pyrites with low 34S/32S ratios in ~3.47-Gyr-old sedimentary barites from North Pole, Australia have been interpreted as evidence for microbial sulfate reduction and/or sulfur disproportionation in the early Archean. We show that these microscopic sulfides have similar to slightly less negative Δ33S and slightly more negative Δ36S values compared to the enclosing sulfate crystals. This finding is consistent with a primary mass-independent signature overprinted by biological sulfate reduction, as calibrated by previous experimental laboratory culture studies. However, it is inconsistent with an overprint by abiological sulfate reduction or sulfur disproportionation, as predicted by isotope exchange theory and laboratory culture studies. Thus, our multiple sulfur isotope measurements support the contention that sulfate-reducing microbes had evolved by ~3.47 billion years ago. [Copyright &y& Elsevier]

A detailed study of the size distribution of framboidal pyrites in the black shales of the Upper Permian Ravnefjeld Formation was performed to evaluate the redox state of the Late Permian ocean. In contrast to framboidal pyrites in bioturbated sediments, the smaller and less variable size distribution of pyrite framboids in the laminated shales of the Ravnefjeld Formation provides persuasive evidence for sulfidic (H2S-rich) bottom-water conditions in the East Greenland Basin. However, the S isotope compositions of both pyrite populations show a similar distribution. The widespread BMS values of pyrites (-41.2‰ to -28.2‰) in the black shales of the Ravnefjeld Formation indicate a large fractionation (up to 52.7‰) relative to seawater sulfate, and may record different pathways of sulfur cycling in sulfidic water columns as well as within sediments. The new data from the East Greenland Basin indicate that environmental stress such as widespread sulfidic conditions could have caused the biotic crisis in the Late Permian. [ABSTRACT FROM AUTHOR]

In this study, we report multiple S-isotopic data (δ34S and Δ33S) of sedimentary pyrite in Early to Late Ordovician sections from South China. The results reveal two distinct groups of negative Δ33S anomalies during the Dapingian and Sandbian to Early Katian stages, which coincide with two faunal turnover events. The negative Δ33S values reflect the mixing of sulfides with strongly negative δ34S and positive Δ33S, and sulfide with strongly positive δ34S and positive Δ33S. This mixing scenario may have resulted from the impinging of deep anoxic waters onto the continental shelves possibly facilitated by sea-level rise. The temporal co-occurrence of negative Δ33S anomalies with intervals of faunal turnover in brachiopod assemblages of South China suggests that the encroachment of anoxic waters may have driven the diversity crises. Our results provide evidence for a dynamic mechanism linking the recurrent upwelling of deep anoxic waters and faunal turnovers during the Early to Late Ordovician. • First multiple S-isotope study of the Ordovician sedimentary rocks from China. • Negative Δ33S values coincide with faunal turnover events. • Upwelling of deep anoxic waters may have driven the diversity crises. • Constrain the dynamics of marine redox variation during the Ordovician. [ABSTRACT FROM AUTHOR]